1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a column spacer capable of preventing generation of spots on a screen when an LCD panel is touched, and a method of fabricating the same.
2. Discussion of the Related Art
Demands for various display devices have increased with development of the information technology society. Accordingly, many efforts have been made to research and develop various flat display devices such as LCD, plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some species of flat display devices have already been applied to displays for various equipments. Among the various flat display devices, LCD devices have been most widely utilized because of their advantageous characteristics of thin profile, lightness in weight, and low power consumption, and become substitutes for cathode ray tube (CRT) devices. In addition to mobile type LCD devices such as notebook computers, LCD devices have been utilized for computer monitors and televisions receiving and displaying broadcasting signals. While various technical developments in the LCD technology have been applied to different fields, research in enhancing the picture quality of the LCD devices has not reached as far as that in other features and advantages of the LCD device. In order to use LCD devices in various fields as a general display, it is important to develop an LCD device capable of showing a high quality picture with high resolution and high luminance on a large-sized screen, while still maintaining lightness in weight, thin profile, and low power consumption.
Next, a related art LCD device having spacers for maintaining a cell gap between substrates will be described with reference to the accompanying drawings. FIG. 1 is an expanded perspective view illustrating the related art LCD device. As shown in FIG. 1, the LCD device includes first and second substrates 1, 2, and a liquid crystal layer 3 formed between the first and second substrates 1, 2 by injection. Specifically, the first substrate 1 includes a plurality of gate lines 4 arranged along a first direction at fixed intervals, a plurality of data lines 5 arranged along a second direction perpendicular to the first direction at fixed intervals, a plurality of pixel electrodes 6 arranged in a matrix-type configuration within pixel regions P defined by crossing of the gate and data lines 4, 5, and a plurality of thin film transistors T enabled according to signals supplied to the gate lines 4 for transmitting signals from the data lines 5 to the pixel electrodes 6. Also, the second substrate 2 includes a black matrix layer 7 that prevents light from portions of the first substrate 1 except the pixel regions P, an R/G/B color filter layer 8 for displaying various colors, and a common electrode 9 for producing the image on the color filter layer 8. In this related art LCD device, the liquid crystal layer 3 has a plurality of liquid crystal molecules that are driven by an electric field generated between the pixel electrode 6 and the common electrode 9. That is, an alignment direction of the liquid crystal molecules of the liquid crystal layer 3 is controlled by the induced electric field thereto. Accordingly, light irradiated through the liquid crystal layer 3 may be controlled by the alignment direction of the liquid crystal molecules, thereby displaying an image. This kind of LCD device may be referred to as a TN mode LCD device, which has disadvantageous characteristics such as a narrow viewing angle. In order to overcome this problem, an in-plane switching (IPS) mode LCD device has been actively developed, wherein a pixel electrode and a common electrode are formed in a pixel region in parallel to each other at a fixed interval, thereby generating an electric field parallel to substrates between the pixel electrode and the common electrode and aligning liquid crystal molecules of a liquid crystal layer.
Next, a method of fabricating the related art IPS mode LCD device will be described with reference to the accompanying drawings. In general, there are two methods for fabricating an LCD device: a liquid crystal injection method and a liquid crystal dispersion method.
First, the liquid crystal injection method will be described as follows. FIG. 2 is a flow chart illustrating the liquid crystal injection method, which may be divided into three processes: an array process, a cell process, and a module process. The array process mainly includes two steps: forming a TFT array having gate and data lines, a pixel electrode and a thin film transistor on a first substrate, and forming a color filter array having a black matrix layer, a color filter layer and a common electrode on a second substrate. During the array process, a plurality of LCD panel regions are formed on one large glass substrate, and the TFT array and the color filter array are formed in each LCD panel region. After that, the TFT substrate and the color filter substrate are moved to a cell process line. Subsequently, an alignment material is coated on the TFT substrate and the color filter substrate, and an alignment process (rubbing process) S10 is performed to the substrates to obtain a uniform alignment direction in the liquid crystal molecules. At this time, the alignment process S10 is carried out in order of processes for cleaning before deposition of an alignment layer, printing the alignment layer, baking the alignment layer, inspecting the alignment layer and rubbing the alignment layer. Then, at a cleaning process S20, the TFT substrate and the color filter substrate are respectively cleaned. After that, at a spacer scattering process S30, ball spacers for maintaining a cell gap between the two substrates are scattered on one of the two substrates, and then at a sealant coating process S40, a seal pattern is formed corresponding to the circumference of respective LCD panel regions to bond the two substrates to each other. At this time, the seal pattern has a liquid crystal injection inlet through which liquid crystal is injected. The ball spacers are formed of plastic balls or elastic plastic minute particles.
Then, at a bonding/hardening process S50, the TFT substrate and the color filter substrate having the seal pattern therebetween are opposite to each other, and bonded to each other, and then the seal pattern is hardened. After that, at a cutting/processing process S60, the TFT substrate and the color filter substrate bonded to each other are cut into the respective LCD panel regions, thereby fabricating the unit LCD panels each having a fixed size. Subsequently, at an injection/seal process S70, the liquid crystal is injected to the LCD panel through the liquid crystal injection inlet, and then the liquid crystal injection inlet is sealed, thereby forming a liquid crystal layer. Finally, an inspection process S80 is conducted for an external appearance and an electric failure in the LCD panel. Thus, the process of fabricating the LCD device is completed.
Herein, the process for injecting the liquid crystal will be described in brief. First, the LCD panel and a container having liquid crystal material are provided in a chamber which is maintained in a vacuum state. That is, moisture and air bubble are removed simultaneously from the liquid crystal material and the container, and an inside space of the LCD panel is maintained in a vacuum state. Then, a liquid crystal injection inlet of the LCD panel is dipped into the container to change the vacuum state inside the chamber to an atmospheric pressure. Thus, the liquid crystal material is injected to the inside of the LCD panel through the liquid crystal injection inlet according to a pressure difference between the inside the LCD panel and the chamber.
However, the liquid crystal injection method has the following disadvantages. First, after the large glass substrate is cut into the respective LCD panel regions, the liquid crystal injection inlet is dipped into the container having the liquid crystal material while maintaining the vacuum state between the two substrates. Thus, it takes great time in injecting the liquid crystal material between the two substrates, thereby lowering yield. In case of forming a large sized LCD device, it is difficult to completely inject the liquid crystal material into the inside of the LCD panel, thereby causing the failure due to incomplete injection of the liquid crystal material. Furthermore, it takes great time in injecting the liquid crystal material, and it also requires a large space for liquid crystal injection devices.
In order to overcome these problems caused by the liquid crystal injection method, the liquid crystal dispersion method has been proposed, in which two substrates are bonded to each other after dispersing liquid crystal material on any one of the two substrates. FIG. 3 is a flow chart illustrating the liquid crystal dispersion method. In this method, before the two substrates are bonded, the liquid crystal is dispersed on any one of the two substrates. It is impossible to use ball spacers for maintaining a cell gap between the two substrates since the ball spacers move to a dispersion direction of the liquid crystal material. Thus, instead of the ball spacers, patterned spacers or column spacers are fixed to the substrate to maintain the cell gap between the two substrates. That is, as shown in FIG. 3, during an array process, a black matrix layer, a color filter layer and an overcoat layer are formed on the color filter substrate. Then, a photosensitive resin is formed on the overcoat layer, and selectively removed to form the column spacer on the overcoat layer above the black matrix layer. The column spacers may be formed in a photo process or an ink-jet process. After that, alignment layers are respectively coated on entire surfaces of the TFT substrate and the color filter substrate including the column spacers, and a rubbing process is performed thereto.
Then, at a cleaning process S101, the TFT substrate and the color filter substrate are cleaned. At a liquid crystal dispersion process S102, the liquid crystal material is dispersed on one of the two substrates. At a seal pattern dispensing process S103, a seal pattern is formed in the circumference of an LCD panel region on the other of the two substrates by a dispensing device. At this time, it is possible to perform dispersion of the liquid crystal and formation of the seal pattern on any one of the two substrates. At an inversion process S104, the other substrate having no dispersion of the liquid crystal material is inversed.
After that, at a bonding/hardening process S105, the TFT substrate and the color filter substrate are bonded to each other by pressure, and the seal patterned is hardened. Subsequently, at a cutting/processing process S106, the bonded substrates are cut into the respective LCD panels. Finally, an inspection process S107 is conducted for an external appearance and an electric failure in the LCD panel. The process of fabricating the LCD device is thus completed.
FIG. 4 is a cross-sectional view schematically illustrating the related art LCD device on which the column spacers are formed. In FIG. 4, the LCD device includes the color filter substrate 2 on which a plurality of column spacers 20 are formed, and the TFT substrate 1 on which the liquid crystal 3 is dispersed. As mentioned above, the column spacers 20 are fixed to the color filter substrate 2, and the color filter substrate 2 is in contact with the TFT substrate 1. The column spacers 20 each have a flat surface being in contact with the TFT substrate 1. Accordingly, the LCD device fabricated by the liquid crystal injection method includes the spherical ball spacers, and the spherical ball spacers are not fixed to the substrate, whereby it obtains a great restoring force of the liquid crystal even in case of external impacts (pressing, rubbing, or the like). That is, even though the external force is applied for the LCD panel, it does not generate spots on the screen.
However, the related art LCD device using the column spacers has the following disadvantages. First, the column spacers are fixed to one substrate, and the column spacers have the flat surface being in contact with the TFT substrate, thereby causing a great frictional force due to the increase in the contact surface to the substrate. Accordingly, in a case where the screen of the LCD device having the column spacers is rubbed, spots may be generated on the screen for a long time. FIG. 5A and FIG. 5B are a plane view and a cross-sectional view illustrating the spots generated on the screen by touching the LCD panel. If the LCD panel 10 is continuously touched with a finger along a predetermined direction as shown in FIG. 5A, the upper substrate of the LCD panel 10 is shifted at a predetermined interval along the touch direction as shown in FIG. 5B. At this time, in a case where the cylindrical column spacers are in contact with the lower and upper substrates, it causes the great frictional force between the column spacers and the two opposing substrates 1, 2. Thus, the liquid crystal molecules between the column spacers are not restored to the original state, thereby generating the spots on the screen. Also, when the LCD panel is touched with the finger along the predetermined direction as shown in FIG. 5B, the liquid crystal molecules gather to the region around the touch portion, thereby causing the region around the touch portion to protrude. In this case, a cell gap h1 corresponding to a protruding portion is higher than a cell gap h2 of the remaining portions, thereby generating a light leakage. Accordingly, it is impossible to obtain the uniform luminance.
If the amount of liquid crystal material dispersed on the substrate is increased to overcome the problem of the spots on the screen by touch, it may cause another problem due to gravity force. That is, since the LCD device is usually utilized as a display of a monitor, a notebook computer, or a television, the LCD device is usually installed in vertical. Thus, the liquid crystal molecules of the LCD panel may move to the direction of gravity. In particular, when the LCD panel is at a high temperature, the movement of liquid crystal molecules becomes serious because the liquid crystal has great thermal expansion.
The ball spacers are formed in a large amount. However, the column spacers are selectively formed on the portions except for the pixel regions. Accordingly, when the LCD panel is pressed at a predetermined portion having no column spacers, the substrates are bent, and maintained in a hollow state due to low restoring speed, thereby generating spots on the screen.